The present invention relates to a sailing yacht and especially to a pivotally deployable bulb mounted foil for the keel of a sailing yacht which can pivot a foil mounted within a keel bulb remotely as needed to provide lateral resistance for the sailboat.
The use of canting keels on sailing yachts is being widely used around the world because by using hydraulics to “cant” a keel to weather, a boat can develop large extra amounts of righting moment and therefore power to carry sail which translates directly to speed.
If a canting keel is used however, some means must be found to augment the area required by a sailboat for lateral resistance since, as the keel cants, it presents less surface area capable of generating resistance to leeway. Several techniques have been employed to compensate for the loss of lateral resistance. It has been suggested to use twin fore and aft rudders to develop all lateral resistance, reducing the keel to just a ballast holding strut, or twin asymmetrical daggerboards that do the same thing. A single gybing daggerboard has been suggested as has been a system using fixed “wings” attached to the ballast bulb and extending out 90 degrees to the centerline of the boat so that as the keel cants, the fixed foils generate more and more lateral resistance replacing that lost by the keel.
The present invention mounts a pivotable asymmetric (flat on top) foil to the bulb that has been designed specifically to mate with it so that when the foil is not in use, it s pivoted so that its span is in line with the ballast bulb and actually forms a part of the bulb. When deployed, the foil is rotated 90 degrees so that it sticks out 90 degrees to the keel of the boat and the bulb. As the boat heels or the keel cants or both, this foil begins to develop lateral resistance lost to a canting keel or to a “normal” fixed keel when heeled. Then, when lateral resistance is no longer needed, the foil is rotated back to its nesting position, in line with the bulb, and forming the bottom of the bulb. This in effect eliminates the wetted surface and drag of the deployed foil or the fixed foils as in 4 above. Use of this system eliminates the need for twin fore and aft rudders or daggerboards when using a canting keel on a modern sailboat.
The present invention can also be retrofitted to existing yachts to improve windward performance with no wetted surface gain when not in use. It can-be designed into fixed keel sailboats so that the keel area can be reduced using the foil to augment windward performance while allowing improved downwind performance over a standard fixed keel due to the reduction of fin area made possible by the foil.
Control of the foil may be a number of ways such as by use of a shaft that runs through a fixed or canting keel and is adjustable by using a hydraulic motor mounted in the bulb or hydraulic or electric power to turn the shaft attached to the foil. The load on the foil as it is deployed will be light allowing use of minimal power and allowing a design feature to include a clutch such that if the lower (or upper) portion of the foil contacts anything, it would simply pivot.
Prior U.S. Patents for sailboat keel systems include the Burroughs U.S. Pat. No. 4,686,922 which has a pendulum like wing that might develop extra righting moment, at a cost of greater drag, and the Ditmore U.S. Pat. No. 6,453,836 for a foil that rotates about an axis parallel to the centerline of the sailboat. It generates extra lift when angled any number of ways relative to the fixed keel it is mounted to. This system is limited to use on a fixed keel. This system has a constant wetted surface and the system is not retractable. It may be stored behind the keel but it still causes wetted surface drag.
The Dorfman et al. U.S. Pat. No. 4,074,646 shows a method of changing the camber of a keel fin in order to help reduce leeway by making the keel more effective in developing lateral resistance. The Frantl et al. U.S. Pat. No. 5,967,074 allows multiple canting keels whose proximity to each other may cause increased drag. The system allows various combinations of lateral resistance at the cost of increased drag.
The Greene U.S. Pat. No. 4,686,923 is essentially a larger version of the trim tab used on many sailboats with winged keels. The Kelsey U.S. Pat. No. 6,019,059 is a foil that may be pivoted with the primary objective being to develop a combination of lateral resistance and/or lift but allows no decrease in wetted surface when not in use and requires a fixed, vertical fin to be mounted.
The Levi et al. U.S. Pat. No. 6,397,771 is for a method of utilizing a wing-like hydrofoil on a fixed keel such that the fixed keel or centerboard can be retracted to reduce the draft of the boat or to change the fore and aft sailing balance of the boat. While the horizontal foil stays immersed at all times, the vertical keel/centerboard may be partially retracted within the boat hull. The E. L. Morales U.S. Pat. No. 3,324,815 is a high drag device compared to modern foils/hydrofoils.
The Page U.S. Pat. No. 5,152,238 is a split canting keel with a fixed wing attached to either side of the split canting keel which will reduce draft but with increased drag. The E. G. Pollak U.S. Pat. No. 3,080,845 is a flap-like device attached to the back side of a conventional fixed keel and requires mounting on a fixed keel. The F. O. Stromborg U.S. Pat. No. 768,085 is a relatively low aspect ratio keel that can allow some small increase of windward performance offset by an increase in drag associated with the low aspect “blades”.